Phosphorus trichloride

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Phosphorus trichloride
Phosphorus trichloride 25ml.jpg
IUPAC name
Phosphorus trichloride
Systematic IUPAC name
Other names
Phosphorus(III) chloride
Phosphorous chloride
3D model (JSmol)
ECHA InfoCard 100.028.864 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-749-3
PubChem CID
RTECS number
  • TH3675000
UN number 1809
  • InChI=1S/Cl3P/c1-4(2)3 Yes check.svgY
  • ClP(Cl)Cl
Molar mass 137.33 g/mol
AppearanceColorless to yellow fuming liquid [1]
Odor unpleasant, acrid, like hydrochloric acid [1]
Density 1.574 g/cm3
Melting point −93.6 °C (−136.5 °F; 179.6 K)
Boiling point 76.1 °C (169.0 °F; 349.2 K)
Solubility in other solventssoluble[ vague ] in benzene, CS2, ether, chloroform, CCl4, halogenated organic solvents
reacts with ethanol
Vapor pressure 13.3 kPa
63.4·10−6 cm3/mol
1.5122 (21 °C)
Viscosity 0.65 cP (0 °C)
0.438 cP (50 °C)
0.97 D
319.7 kJ/mol
Occupational safety and health (OHS/OSH):
Main hazards
Highly toxic, [2] corrosive
GHS labelling: [3]
GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-acid.svg
H300, H301, H314, H330, H373
P260, P273, P284, P303+P361+P353, P304+P340+P310, P305+P351+P338
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
18 mg/kg (rat, oral) [4]
104 ppm (rat, 4 hr)
50 ppm (guinea pig, 4 hr) [4]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 0.5 ppm (3 mg/m3) [1]
REL (Recommended)
TWA 0.2 ppm (1.5 mg/m3) ST 0.5 ppm (3 mg/m3) [1]
IDLH (Immediate danger)
25 ppm [1]
Safety data sheet (SDS) ICSC 0696
Related compounds
Related phosphorus chlorides
Phosphorus pentachloride
Phosphorus oxychloride
Diphosphorus tetrachloride
Related compounds
Phosphorus trifluoride
Phosphorus tribromide
Phosphorus triiodide
Supplementary data page
Phosphorus trichloride (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic and reacts readily with water to release hydrogen chloride.


Phosphorus trichloride was first prepared in 1808 by the French chemists Joseph Louis Gay-Lussac and Louis Jacques Thénard by heating calomel (Hg2Cl2) with phosphorus. [5] Later during the same year, the English chemist Humphry Davy produced phosphorus trichloride by burning phosphorus in chlorine gas. [6]


World production exceeds one-third of a million tonnes. [7] Phosphorus trichloride is prepared industrially by the reaction of chlorine with white phosphorus, using phosphorus trichloride as the solvent. In this continuous process PCl3 is removed as it is formed in order to avoid the formation of PCl5.

P4 + 6 Cl2 → 4 PCl3

Structure and spectroscopy

It has a trigonal pyramidal shape. Its 31P NMR spectrum exhibits a singlet around +220 ppm with reference to a phosphoric acid standard.[ citation needed ]


The phosphorus in PCl3 is often considered to have the +3 oxidation state and the chlorine atoms are considered to be in the 1 oxidation state. Most of its reactivity is consistent with this description.[ citation needed ]


PCl3 is a precursor to other phosphorus compounds, undergoing oxidation to phosphorus pentachloride (PCl5), thiophosphoryl chloride (PSCl3), or phosphorus oxychloride (POCl3).

PCl3 as an electrophile

Phosphorus trichloride is the precursor to organophosphorus compounds that contain one or more P(III) atoms, most notably phosphites and phosphonates. These compounds do not usually contain the chlorine atoms found in PCl3.

PCl3 reacts vigorously with water to form phosphorous acid (H3PO3) and hydrochloric acid:

PCl3 + 3 H2O → H3PO3 + 3 HCl

A large number of similar substitution reactions are known, the most important of which is the formation of phosphites by reaction with alcohols and phenols. For example, with phenol, triphenyl phosphite is formed:

3 PhOH + PCl3 → P(OPh)3 + 3 HCl

where "Ph" stands for the phenyl group, -C6H5. Alcohols such as ethanol react similarly in the presence of a base such as a tertiary amine: [8]

PCl3 + 3 EtOH + 3 R3N → P(OEt)3 + 3 R3NH+Cl

In the absence of base, however, the reaction proceeds with the following stoichiometry to give diethylphosphite: [9] [10]

PCl3 + 3 EtOH → (EtO)2P(O)H + 2 HCl + EtCl

Secondary amines (R2NH) form aminophosphines. For example, bis(diethylamino)chlorophosphine, (Et2N)2PCl, is obtained from diethylamine and PCl3. Thiols (RSH) form P(SR)3. An industrially relevant reaction of PCl3 with amines is phosphonomethylation, which employs formaldehyde:

R2NH + PCl3 + CH2O → (HO)2P(O)CH2NR2 + 3 HCl

Aminophosphonates are widely used as sequestering and antiscale agents in water treatment. The large volume herbicide glyphosate is also produced this way. The reaction of PCl3 with Grignard reagents and organolithium reagents is a useful method for the preparation of organic phosphines with the formula R3P (sometimes called phosphanes) such as triphenylphosphine, Ph3P.

3 PhMgBr + PCl3 → Ph3P + 3 MgBrCl

Under controlled conditions or especially with bulky organic groups, similar reactions afford less substituted derivatives such as chlorodiisopropylphosphine.

PCl3 as a nucleophile

Phosphorus trichloride has a lone pair, and therefore can act as a Lewis base, [11] e.g., forming a 1:1 adduct Br3B-PCl3. Metal complexes such as Ni(PCl3)4 are known, again demonstrating the ligand properties of PCl3.

This Lewis basicity is exploited in the Kinnear–Perren reaction to prepare alkylphosphonyl dichlorides (RP(O)Cl2) and alkylphosphonate esters (RP(O)(OR')2). Alkylation of phosphorus trichloride is effected in the presence of aluminium trichloride give the alkyltrichlorophosphonium salts, which are versatile intermediates: [12]

PCl3 + RCl + AlCl3 → RPCl+
+ AlCl

The RPCl+
product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl2.

PCl3 as a ligand

PCl3, like the more popular phosphorus trifluoride, is a ligand in coordination chemistry. One example is Mo(CO)5PCl3. [13]


PCl3 is important indirectly as a precursor to PCl5, POCl3 and PSCl3, which are used in many applications, including herbicides, insecticides, plasticisers, oil additives, and flame retardants.

For example, oxidation of PCl3 gives POCl3, which is used for the manufacture of triphenyl phosphate and tricresyl phosphate, which find application as flame retardants and plasticisers for PVC. They are also used to make insecticides such as diazinon. Phosphonates include the herbicide glyphosate.

PCl3 is the precursor to triphenylphosphine for the Wittig reaction, and phosphite esters which may be used as industrial intermediates, or used in the Horner-Wadsworth-Emmons reaction, both important methods for making alkenes. It can be used to make trioctylphosphine oxide (TOPO), used as an extraction agent, although TOPO is usually made via the corresponding phosphine.

PCl3 is also used directly as a reagent in organic synthesis. It is used to convert primary and secondary alcohols into alkyl chlorides, or carboxylic acids into acyl chlorides, although thionyl chloride generally gives better yields than PCl3. [14]


Industrial production of phosphorus trichloride is controlled under the Chemical Weapons Convention, where it is listed in schedule 3, as it can be used to produce mustard agents. [19]

See also

Related Research Articles

<span class="mw-page-title-main">Chlorine</span> Chemical element, symbol Cl and atomic number 17

Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine.

The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.

In organic chemistry, an acyl chloride is an organic compound with the functional group −C(=O)Cl. Their formula is usually written R−COCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.

An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class provides common examples. The wide structural variety and divergent chemical properties of organochlorides lead to a broad range of names, applications, and properties. Organochlorine compounds have wide use in many applications, though some are of profound environmental concern, with TCDD being one of the most notorious.

<span class="mw-page-title-main">Aluminium chloride</span> Chemical compound

Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both are colourless crystals, but samples are often contaminated with iron(III) chloride, giving a yellow color.

<span class="mw-page-title-main">Acetyl chloride</span> Organic compound (CH₃COCl)

Acetyl chloride is an acyl chloride derived from acetic acid. It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl.

<span class="mw-page-title-main">Thionyl chloride</span> Inorganic compound (SOCl2)

Thionyl chloride is an inorganic compound with the chemical formula SOCl2. It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes per year being produced during the early 1990s, but is occasionally also used as a solvent. It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons.

In polyatomic cations with the chemical formula PR+
. These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions.

<span class="mw-page-title-main">Phosphorus pentachloride</span> Chemical compound

Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moisture-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.

Phosphorous acid (or phosphonic acid (singular)) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Organic derivatives of phosphorous acid, compounds with the formula RPO3H2, are called phosphonic acids.

<span class="mw-page-title-main">Tantalum(V) chloride</span> Chemical compound

Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl3) and eventually tantalum pentoxide (Ta2O5); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.

<span class="mw-page-title-main">Phosphoryl chloride</span> Chemical compound

Phosphoryl chloride is a colourless liquid with the formula POCl3. It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosphorus trichloride and oxygen or phosphorus pentoxide. It is mainly used to make phosphate esters such as tricresyl phosphate.

<span class="mw-page-title-main">Phosphite ester</span> Organic compound with the formula P(OR)3

In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of an unobserved tautomer phosphorous acid, H3PO3, with the simplest example being trimethylphosphite, P(OCH3)3. Some phosphites can be considered esters of the dominant tautomer of phosphorous acid (HP(O)(OH)2). The simplest representative is dimethylphosphite with the formula HP(O)(OCH3)2. Both classes of phosphites are usually colorless liquids.

Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.

<span class="mw-page-title-main">Antimony pentachloride</span> Chemical compound

Antimony pentachloride is a chemical compound with the formula SbCl5. It is a colourless oil, but typical samples are yellowish due to dissolved chlorine. Owing to its tendency to hydrolyse to hydrochloric acid, SbCl5 is a highly corrosive substance and must be stored in glass or PTFE containers.

<span class="mw-page-title-main">Arsenic trichloride</span> Chemical compound

Arsenic trichloride is an inorganic compound with the formula AsCl3, also known as arsenous chloride or butter of arsenic. This poisonous oil is colourless, although impure samples may appear yellow. It is an intermediate in the manufacture of organoarsenic compounds.

<span class="mw-page-title-main">Hexachlorophosphazene</span> Chemical compound

Hexachlorophosphazene is an inorganic compound with the formula (NPCl2)3. The molecule has a cyclic, unsaturated backbone consisting of alternating phosphorus and nitrogen centers, and can be viewed as a trimer of the hypothetical compound N≡PCl2. Its classification as a phosphazene highlights its relationship to benzene. There is large academic interest in the compound relating to the phosphorus-nitrogen bonding and phosphorus reactivity.

<span class="mw-page-title-main">Thiophosphoryl chloride</span> Chemical compound

Thiophosphoryl chloride is an inorganic compound with the formula PSCl3. It is a colorless pungent smelling liquid that fumes in air. It is synthesized from phosphorus chloride and used to thiophosphorylate organic compounds, such as to produce insecticides.

<span class="mw-page-title-main">Trimethyl phosphite</span> Chemical compound

Trimethyl phosphite is an organophosphorus compound with the formula P(OCH3)3, often abbreviated P(OMe)3. It is a colorless liquid with a highly pungent odor. It is the simplest phosphite ester and finds used as a ligand in organometallic chemistry and as a reagent in organic synthesis. The molecule features a pyramidal phosphorus(III) center bound to three methoxy groups.

<span class="mw-page-title-main">Phosphoryl chloride difluoride</span> Chemical compound

Phosphoric chloride difluoride POF2Cl is a colourless gas. At one atmosphere pressure the gas condenses to a liquid at 3.1°C and freezes at −96.4. Alternate names are difluorophosphoryl chloride or phosphoryl chloride difluoride.


  1. 1 2 3 4 5 NIOSH Pocket Guide to Chemical Hazards. "#0511". National Institute for Occupational Safety and Health (NIOSH).
  2. Phosphorus trichloride toxicity
  3. Sigma-Aldrich Co., Phosphorus trichloride.
  4. 1 2 "Phosphorus trichloride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. Gay-Lussac; Thénard (27 May 1808). "Extrait de plusieurs notes sur les métaux de la potasse et de la soude, lues à l'Institut depuis le 12 janvier jusqu'au 16 mai" [Extracts from several notes on the metals potassium and sodium, read at the Institute from the 12th of January to the 16th of May]. Gazette Nationale, Ou le Moniteur Universel (in French). 40 (148): 581–582. From p. 582: "Seulement ils ont rapporté qu'en traitant le mercure doux par le phosphure, dans l'espérance d'avoir de l'acide muriatique bien sec, il ont trouvé une liqueur nouvelle très limpide, sans couleur, répandant de fortes vapeurs, s'enflammant spontanément lorsqu'on en imbibe le papier joseph; laquelle ne paraît être qu'une combinaison de phosphore, d'oxigène et d'acide muriatique, et par conséquent analogue à cette qu'on obtient en traitant le soufre par le gas acide muriatique oxigèné." (Only they reported that by treating calomel with phosphorus, in the hope of obtaining very dry hydrogen chloride, they found a new, very clear liquid, colorless, giving off strong vapors, spontaneously igniting when one soaks filter paper in it; which seems to be only a compound of phosphorus, oxygen, and hydrochloric acid, and thus analogous to what one obtains by treating sulfur with chlorine gas.)
  6. Davy, Humphry (1809). "The Bakerian Lecture. An account of some new analytical researches on the nature of certain bodies, particularly the alkalies, phosphorus, sulphur, carbonaceous matter, and the acids hitherto undecomposed; with some general observations on chemical theory". Philosophical Transactions of the Royal Society of London. 99: 39–104. doi:10.1098/rstl.1809.0005. S2CID   98814859. On pp. 94–95, Davy mentioned that when he burned phosphorus in chlorine gas ("oxymuriatic acid gas"), he obtained a clear liquid (phosphorus trichloride) and a white solid (phosphorus pentachloride).
  7. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  8. A. H. Ford-Moore & B. J. Perry (1963). "Triethyl Phosphite". Organic Syntheses .; Collective Volume, vol. 4, p. 955
  9. Malowan, John E. (1953). "Diethyl phosphite". Inorganic Syntheses. Inorganic Syntheses. Vol. 4. pp. 58–60. doi:10.1002/9780470132357.ch19. ISBN   9780470132357.
  10. Pedrosa, Leandro (2011). "Esterification of Phosphorus Trichloride with Alcohols; Diisopropyl phosphonate". ChemSpider Synthetic Pages. Royal Society of Chemistry: 488. doi: 10.1039/SP488 .
  11. R. R. Holmes (1960). "An examination of the basic nature of the trihalides of phosphorus, arsenic and antimony". Journal of Inorganic and Nuclear Chemistry. 12 (3–4): 266–275. doi:10.1016/0022-1902(60)80372-7.
  12. Svara, J.; Weferling, N.; Hofmann, T. "Phosphorus Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_545.pub2.
  13. Frenking, Gernot; Wichmann, Karin; Fröhlich, Nikolaus; Grobe, Joseph; Golla, Winfried; Van, Duc Le; Krebs, Bernt; Läge, Mechtild (2002). "Nature of the Metal−Ligand Bond in M(CO)5PX3 Complexes (M = Cr, Mo, W; X = H, Me, F, Cl): Synthesis, Molecular Structure, and Quantum-Chemical Calculations". Organometallics. 21 (14): 2921–2930. doi:10.1021/om020311d.
  14. L. G. Wade Jr. (2005). Organic Chemistry (6th ed.). Upper Saddle River, New Jersey, USA: Pearson/Prentice Hall. p. 477.
  15. A. D. F. Toy (1973). The Chemistry of Phosphorus. Oxford, UK: Pergamon Press.
  16. Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)
  17. OSHA: Phosphorus Trichloride
  18. CDC - NIOSH Pocket Guide to Chemical Hazards
  19. M. C. Forbes; C. A. Roswell; R. N. Maxson (1946). Phosphorus(III) Chloride. Inorg. Synth. Inorganic Syntheses. Vol. 2. pp. 145–7. doi:10.1002/9780470132333.ch42. ISBN   9780470132333.